Portable electrical tool having permanent magnet field



July 7, 1970 'P. H. MORGANSON PORTABLE ELECTRICAL TOOL HAVING PERMANENT MAGNET FIELD Filed March 13, 1967 INVENTOR.

PETER H. MORGANSON ATTOR N EYS United States Patent 3 519 858 PORTABLE ELEcTRIbAL TOOL HAVING PERMANENT MAGNET FIELD Peter H. Morganson, Winsted, Conn., assignor to The Stanley Works, New Britain, Conn., a corporation of 5 Connecticut Filed Mar. 13, 1967, Ser. No. 622,485 Int. Cl. H02k 7/14 US. Cl. 310-47 1 Claim ABSTRACT OF THE DISCLOSURE This invention generally relates to portable electrical tools and has as a primary object the provision of an improved power tool which incorporates a novel housing construction of significantly reduced size for greater convenience in handling and which provides high power performance and reliability normally associated with larger and heavier tools.

Another object of the invention is to provide an improved power tool of the above described type having a simplified construction utilizing a minimum number of parts particularly suited for the manufacture of several versions of a hand manipulatable light weight, electrically operated power tool by interchanging one or more subassemblies of the basic tool.

A further object of the invention is to provide an improved power tool which, in addition to being compact and powerful, is of pleasing appearance and rugged construction for dependable use over a long service life.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which. will be exemplified in the construction hereafter set forth and the scope of the application which will be indicated in the appended claim.

In the drawing:

FIG. 1 is a side elevational view, partly broken away and partly in section, showing a hand drill incorporating the present invention; and

FIG. 2 is a transverse section view taken generally along line 2-2 of FIG 1.

Referring now to the drawing in detail, a preferred embodiment of a hand drill constructed in accordance with the invention is shown having a multiple part housing comprising a cylindrical motor housing 10 having forward and rear ends secured to a nose portion or gear housing -12 and to a pistol-grip handle portion or housing 14.

The handle housing 14 is formed by a switch handle 16 and a complementary switch handle cover 18 releasably fixed thereto by suitable screws such as that shown at 20. A strain relief 22 is illustrated at the base of the handle housing 14 for protecting an electric cord 24 at its entrance into the tool.

Upon connecting the cord 24 to a source of electrical power, not shown, a rotary electrical motor 26 is energized through a rectifier 27, either full or one-half wave, and through a double-pole, double-throw switch 28, upon actuation of a trigger switch 30 mounted in the handle housing 14 for suitable connection to switch 28. For the convenience of an operator, switch 28 is seated in the upper rear end of the switch handle cover 18 whereby the operator can reverse motor rotation by simply moving his thumb across a switch button 31 in a one handed operation.

The motor 26 includes a rotor comprising a conventionally wound, laminated armature 32 and a commutator 34 coaxially mounted on a motor shaft 36 having opposite end portions supported for rotation in forward and rear bearing assemblies 38, 40 suitably mounted in the gear housing 12 and the handle housing 14. Upper and lower brush assemblies 42, 44 are mounted in the handle housing 14 for sliding contact with commutator segments and are electrically connected in a well-known manner to the switch 28 for selectively operating the rotor in both rotational directions in accordance with the desired direction of rotation. As will be well understood by one in the art brush 44 is of a greater length than that of brush 42 to compensate for more rapid wear and thereby to provide for balanced brush life.

The forward end of the motor shaft 36 is machined to provide a drive gear 46 in mesh with a pair of driven gears 48, 50 to form a planetary gear arrangement effecting a suitable gear reduction transmitting rotary movement of the motor shaft 36 to a spindle 52, the latter supporting the driven gears 48, 50 for rotation within a gear case 54 threadably secured inside the gear housing 12. Attached to the gear case 54 is a tool holder or chuck housing 56 having an axial passageway 58 in which a chuck and driven clutch half 60 and a positive drive clutch half 62 are shown mounted for operation with the drive clutch half 62 firmly secured to the spindle 52. A plastic double shrouded fan 64, press fit on the motor shaft 36 adjacent the forward end of the armature 32, directs cooling air over the entire length of the armature 32 from inlet openings, not shown, in the handle housing 14 to exhaust through outlet openings 66 circumferentially spaced around the gear housing 12.

To provide a versatile, high performance power tool of compact size in accordance with the present invention, a flux conducting cylinder or sleeve 70 is associated with the motor 26 and is provided with a pair of permanent magnet cylindrical segments 72, 74, symmetrically fixed by any suitable means in direct engagement with an inside surface 76 of the sleeve 70, to jointly serve as an external housing and as a stator for the motor 26 thereby at once minimizing the number of parts while yet providing the necessary magnetic field and a flux shield for the motor 26. The sleeve 70 is fabricated from a suitable magnetic material having low reluctance and negligible magnetic retentivity in contrast to the permanent magnet segments 72, '74 which are formed of any suitable commercially available material exhibiting characteristics of high coercive force and very high magnetic retentivity.

Since there is no external housing element separate from the sleeve 70 which is completely exposed over its entire area, the above described construction provides for a substantial reduction in the over-all size and weight of the tool while yet providing a stator of sufficient field strength to effect high performance operation from noload to full-load conditions heretofore associated with larger and heavier power tools.

To minimize any possibility of dirt, grit and similar undesirable particles entering the tool, the preferred embodiment of the sleeve 70 is formed as a continuous, onepiece imperforate member which will also essentially eliminate chips and shavings, even those of ferromagnetic material, e.g., from becoming lodged inside the motor housing 10.

The above described construction ensures maximum air flow throughout the tool by the provision of the aforementioned double shrouded fan and relatively large air openings whereby the tool will remain comfortably cool even during extended operation thereof. 1

The present invention is particularly suited for quick and easy manufacture and assembly such that the assembled motor 26 may be arranged in proper position and readily secured to the gear housing 12 and the switch handle 16. Opposite axial ends of the sleeve 70 are shown as being of reduced thickness providing annular flanges 78, 80 for abutting engagement with conforming stepped portions circumferentially formed around the rear end of the gear housing 12 and the forward end of the switch handle 16. Before the switch handle cover 18 is fixed in position, the motor housing 10 is firmly secured upon drawing up the gear housing 12 and the switch handle 16 tightly against the projecting flanges 78, 80 of the sleeve 70 by means of a pair of elongated screws 82, 84 extended axially of the motor shaft 36 through open ings 86, 88 (FIG. 2) formed between the permanent magnet segments 72, 74. Screws 82, 84 are thus positioned in diametrically opposed relation between the sleeve 70 and the armature 32 with opposite ends of each screw being secured to housings 12 and 14. Only two holes in the gear housing 12 and the switch handle 16 are required for the screws 82, 84 to properly secure the motor housing 10.

By virtue of this construction, the screws 82, 84 constitute the sole connection for maintaining housings 12, 14 in assembled abutting engagement with opposite axial ends of the sleeve 70, thereby significantly facilitating manufacture and assembly of the tool. Moreover, it will be seen that the above described structure is particularly suited for quick and easy interchanging of one or more subassemblies, e.g., by the attachment of a different nose portion to provide a desired speed change by varying the gear ratio or by similarly adapting the power tool for a variety of work performing operations such as those performed by power wrenches, screwdrivers, drills etc. and thus readily provide several versions of a basic power tool product.

It will also be noted that the motor housing arrangement of this invention permits the motor shaft 36 to be mounted in coaxial alignment with the tool holder 56 to further minimize the space requirements of the drive train components and to ensure an exceptionally compace over-all tool size. While the construction is of notable simplicity and incorporates a minimum number of parts providing cost saving economies in its manufacture and assembly, high power performance is ensured without requiring the usual secondary housing components and other connecting parts commonly associated with conventional tools of this type. In addition, the assembled tool is of rugged and durable construction and yet presents an attractive, streamlined appearance.

As will be apparent to persons skilled in the art, various modifications and adaptations of the structure above described will become readily apparent without departure from the spirit and scope of the invention, the scope of which is defined in the appended claim.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A compact portable hand manipulatable, lightweight, electrically operated power tool energizable from a source of electrical power and comprising a handle portion, a nose portion, a reversible electrical motor including a rotor having opposite ends supported for rotation in said handle portion and said nose portion, a continuous imperforate cylinder, formed of magnetic material of low reluctance and negligible magnetic retentivity, coaxially surrounding said rotor, and a pair of cylindrical segments, formed of permanent magnet material of high coercive force and high magnetic retentivity, fixed to an inside surface of said cylinder in direct engagement therewith and symmetrically arranged thereon radially outwardly of said rotor for providing a magnetic field, said cylinder having an outside surface completely exposed over its entire area and constructing an external motor housing as well as providing a flux shield for said permanent magnet segments, a pair of elongated screws positioned radially inwardly of said cylinder in diametrically opposed relation between said pair of permanent magnet segments, said screws each extending axially of said sleeve and having opposite ends secured to said handle portion and said nose portion and comprising the sole connection for maintaining the same in assembled clamping engagement with opposite axial ends of said cylinder, said nose portion including a tool holder having an axial tool-receiving passageway in coaxial alignment with said cylinder, said handle portion and said nose portion respectively having air inlet openings and air outlet openings formed therein, a fan rotatably coupled to said rotor and positioned in said nose portion for directing cooling air from said air inlet openings through said cylinder to exhaust through said air outlet openings, and hand operated switch means mounted in said handle portion for energizing said motor in opposite rotational directions from a source of electrical power.

References Cited UNITED STATES PATENTS 2,062,938 12/1936 Ruppe l7l-252 2,552,023 5/1951 Andersen 310-50 X 2,876,369 3/1959 Doerner 3l0-50 X 3,213,303 10/1965 Riley 3l089 X 3,215,875 11/1965 Latta 3lO154 3,321,650 5/1967 Pedone 3 l050 X 3,344,291 9/1967 Pratt 31089 X ORIS L. RADER, Primary Examiner K. L. CROSSON, Assistant Examiner US. Cl. X.R. 

